1. Field of the Invention
The present invention relates to a substrate cleaning device and, more particularly, to a substrate cleaning device which prevents a megasonic power from being locally concentrated on a substrate.
2. Description of the Related Art
In general, a semiconductor manufacturing process requires a cleaning process which cleans organics, particles, metallic ions, oxides, from the surface of a semiconductor wafer. Since such contaminants affect the quality and manufacturing yield of the semiconductors, contamination management is very strictly controlled.
The cleaning process is performed frequently during about 40% of the entire semiconductor manufacturing process. It is an essential part of the semiconductor manufacturing process to maintain an ultra-clean wafer since this is required in an ultra large scale integration (ULSI) technique.
As for this cleaning process, a mechanical method, a chemical method, or an ultrasonic method have traditionally been used. Now, as a further technique used to remove contaminants having a size less than micron is a megasonic method. This latter method uses a megasonic process that employs high frequency sound wave. This has attracted substantial public attention due to its high cleaning efficiency and safety.
In the case of a wet batch method, a cassette having wafers is immersed in a bath filled with a cleaning compound, and a megasonic sound wave having a high frequency (about 1 MHz) is generated. In this way, megasonic energy is transferred to the surface of the wafer in parallel through the cleaning compound.
However, the wet batch method has a problem in that a substantial amount of time is required. This is because the cassette is immersed into several bathes in sequence which are in turn used for wafer cleaning. This leads to a very large-sized cleaning device.
A single wafer spin method can be employed instead of the wet batch method. As one example, the single wafer spin method is disclosed in U.S. Patent Publication No. 20030015216(“US '216”). According to US '216, a megasonic probe with a probe shaft extends generally parallel to a surface of a rotating substrate. At least one dispenser applies a cleaning liquid onto the surface of the substrate. The megasonic probe agitates the liquid on the surface.
However, there is a problem with the process of US '216 in that the megasonic probe cannot be used when a pattern size is less than 90 nm because pattern damage occurs due to the megasonic wave. As shown in, FIG. 1 of US '216, a cleaning solution 5 is supplied onto the surface of a substrate 1 by a cleaning solution supplying nozzle (not shown), and a megasonic probe shaft 3 vibrates to agitate the cleaning solution 5 on the substrate 1, thereby performing a cleaning process. Here, a megasonic wave is locally concentrated on a portion A of the substrate 1 below the megasonic probe shaft 3 as compared to the adjacent portions of the substrate 1. This leads to damage of the substrate 1.